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Fluorescence decay time and yield of trans-trans diphenylbutadiene in methylcyclohexane/isohexane and propylene glycol were measured between −50 and +50°C. The radiative rate parameter is independent of solvent and temperature, with a mean value of 8.2 × 108 s−1. This is similar to trans-stilbene but unlike longer polyenes, and is consistent with emission from 1B*u rather than the low-lying 1Ag*g state.

The fluorescence spectra, quantum yields and lifetimes of [10]-, [11]-, [12]-, [13]-, and [14]-helicene and 3,15-ethanoheptahelicene have been observed in 1,4-dioxan solution at room temperature. The fluorescence occurs from the 1 L b state, which is not observed in absorption. The fluoroscence rate parameter decreases with increase in ring number N , in a manner which depends on whether N is odd or even. The intersystem crossing rate parameter increases with N up to N = 11 and then decreases. The interval between the fluorescence maxima, which is equated to the S o symmetrical vibrational mode, decreases from 1200 cm −1 ( N = 6) to 650 cm −1 ( N = 13).

The kinetics of photophysical processes has been measured in stilbene solutions in the temperature range between −40°C and 20°C. The population of the S 1 level excited by two-photon absorption (TPA) and of secondary populated levels has been investigated using a probe beam method. It was found an energy barrier Δ E = 5 × 10 2 cm −1 of the thermically activated transition S 1 → 1′. The rate parameter of this transition is determined to be k −1 11′ , ≈ 2 ps at very high temperatures.

The existence of a compensation law correlating the pre-exponential factor and the activation energy of the rate parameter for internal quenching of fluorescence is established and explained using theoretical results obtained by Lin. Arguments in favour of S 1 ⇝ T 1 intersystem crossing as the dominating process in non-radiative decay, are presented.

Charge pair recombination in anhydrous nitrate ion glass involves mobile N0 3 and probably N0 2− 3 . Charge pairs appear to be coulombically uncorrelated. Kinetics are second order with superimposed time dependence of the rate parameter which arises trom the effect of dielectric relaxation on the activation energy for hopping.